Conventionally, there are provided digital cellular systems such as PDC (Personal Digital Cellular telecommunication system) and PHS (Personal Handyphone System). Upon receipt of incoming calls, portable telephone terminals such as cellular phones held by users produce incoming call sounds to notify users of reception of incoming calls. As incoming call sounds, telephone terminal devices conventionally produce beep sounds, which are offensive to ears of users. Recently, telephone terminal devices produce melody sounds as incoming call sounds instead of the conventional beep sounds.
The aforementioned telephone terminal devices are capable of producing melody sounds, however, which are not satisfactory in sound quality.
In order to improve the sound quality, music playback devices that reproduce music data representing musical tunes on telephone terminal devices are provided. A typical example of a music playback device for use in a telephone terminal device is constituted by a central processing unit (CPU), a read-only memory (ROM), a random-access memory (RAM), and a sound source. Herein, the CPU runs automatic performance programs stored in the ROM, so that music data stored in the ROM or RAM are read, and tone-generation parameters are set to the sound source. Thus, musical tunes are played back on the telephone terminal device.
It is required that telephone terminal devices, particularly portable telephones sold in the market, are reduced in size and price and are designed to have multiple functions. In addition, it is required that telephone terminal devices are capable of performing numerous functions such as call transmission and reception functions, display function, etc. In the music playback device incorporated into the portable telephone terminal device, the CPU should perform music playback processes in addition to telephone function processes. Hence, the music playback device requires a high-speed CPU for processing. This raises a problem in that the portable telephone terminal device having a high-speed CPU must be expensive.
Melody ICs are known as devices that are exclusively designed to reproduce melodies. A typical example of a melody IC for use in a portable telephone terminal device is constituted by a sound source, a sequencer, and a ROM that is exclusively used as a music data storage. By applying music playback instructions from the external device, the melody IC reproduces music data stored in the ROM to play back a melody of a musical tune. By incorporating such a melody IC into the portable telephone terminal device, the CPU does not necessarily perform music playback processes. Using the melody IC eliminates the necessity that the CPU executes music playback processes. Hence, it is possible to use a low-cost and low-speed CPU for the portable telephone terminal device incorporating the melody IC.
Normally, the melody IC provides a ROM having a small storage capacity for music data, hence, the melody IC is capable of storing the limited number of musical tunes, so it is impossible to increase time lengths for playback of musical tunes. Because of the small storage capacity of the ROM, the melody IC cannot store the considerable amount of music data realizing high-quality playback of musical tunes. Hence, the portable telephone terminal device incorporating the melody IC plays back only a melody of low sound quality.
It is an object of the present invention to provide a music playback device that is capable of reproducing musical tunes in high sound quality on the basis of music data stored in the limited storage capacity by using a low-speed operational processor. In addition, it is another object of the present invention to provide a portable telephone terminal device incorporating a music playback device realizing high-quality playback of musical tunes by using the limited storage capacity for music data and by using a low-speed operational processor.